1. Field of the Invention
The present invention relates to information processing methods and systems, and in particular, to a method of limiting the use of information transmitted to a large number of unspecified people solely to a specific user, and a system utilizing such a method. The present invention is very useful in a case where a charge is to be made for information supplied through a communication system.
2. Related Background Art
Presently, the transmission of information using an electromagnetic wave is widely employed, and a telephone and so forth are used as a one-to-one information transmission means. Television, radio and the like are known as unidirectional information transmission means in which information is transmitted from an information transmission source to a large number of unspecified users having individual receivers. In the case of a telecast, a charge for information transmitted to each of the unspecified users is conducted, for example, by collecting a TV reception rate from users having TV receivers by Nippon Hoso Kyokai (NHK) or the Japan Broadcast Association. Further, a charge-based broadcast satellite (BS) broadcast has recently been started by Nippon Eisei Hoso (Japan BS Broadcast) Co., and a charge for this BS broadcast is conducted by using a BS decoder.
FIG. 1 shows a block diagram of an example of the BS decoder. In FIG. 1, a work key (Kw), individual information such as conditions of a reception contract and a master key (Kmi) are stored in a BS decoder 38 which is loaned to a user having a reception contract. In FIG. 1, an initially scrambled (coded or ciphered) video signal is supplied from a BS tuner (not shown) to a video descrambler 37. In addition, a signal comprising information needed for decoding (hereinafter referred to as related information) superimposed on a scrambled audio signal is supplied to a separation circuit 30, and the scrambled audio signal and the related information are separated from each other. The related information is further separated into common information and individual information. The common information consists of a scramble key (Ks) needed to decode the broadcast signal, and contract information, which comprises broadcast station identification information, service contents and so forth, all of which are coded. The separated common information is decoded in a decoding circuit 31, using a work key Kw which is recorded in the BS decoder 38. The contract information is supplied to a contract condition comparison circuit 34 and compared with the contract contents stored in the decoder 38.
On the other hand, a scramble key Ks, which is decoded by the decoding circuit 31, is supplied to a pseudo-random number (PN) generator 35, and the PN generator 35 generates a pseudo-random number signal (PN signal) which has an initial value of Ks when the comparison in the contract condition comparison circuit 34 is satisfied. The PN signal is supplied to an audio descrambler 36 and the video descrambler 37, and the audio and vide signals are respectively decoded using the PN signal.
The individual information is coded information to be used when the contract condition is altered and to be decoded in a decoding circuit 32 using a master key Kmi 33 to re-write the contract condition recorded in the contract condition comparison circuit 34. Thus, the scrambled (coded) video and audio signals are decoded, and only a contractor can receive a broadcast picture image. As a result, the charge is conducted only for the contractor of the BS broadcast, and a change of the contract condition can be performed by the broadcast.
In the prior art pay BS broadcast, however, a charge is conducted for the use of a device of the BS decoder 38 lent to the contractor, and no charge is made for respective groups of information. That is, in the prior art technique, no charge can be conducted individually for respective groups of information, and so it is difficult to make a charge for the particular information received.